The invention relates generally to the field of apparatus having environmentally controllable chambers, such as devices for stressing or testing electronic circuit components. More particularly, the present invention relates to a removable panel for use with such apparatus, and still more particularly, to a door having an expandable portion for use with apparatus for burning-in and testing circuit components.
Integrated (IC) circuit packages and other semiconducter products are mass-produced and installed in electronic circuits within highly sophisticated, complex and costly equipment. As with many mass-produced products, IC packages are prone to failure, in some cases within the first one thousand hours of operation. The complexity of equipment within which such packages are installed makes post-installation failures highly undesirable. For example, when equipment reaches the final inspection stage of production, before failures are detected, the high level skills required for inspection and repair add a significant cost to production expenses. Even more significantly, when the product has been installed in the field and a service technician must make warranty repairs, the costs thereby incurred can have a significant effect on profitability. More and more often, however, post-installation failures simply cannot be tolerated because of the potentially disastrous consequences. As a result, manufacturers of electronic equipment are demanding ever greater quality and dependability in commercial grade IC packages.
Quality and dependability are enhanced substantially by early detection of those IC packages likely to fail early, prior to the installation of the IC packages in equipment. One method for detecting flawed IC packages is referred to as "burn in." "Burn-in" generally involves a technique for stressing and possibly also testing IC packages within their physical and electrical limits to discover IC packages that may be prone to early failure, or to enable the grading and sorting of IC packages according to performance specifications. One burn-in technique includes loading a large number of IC packages into sockets on numerous printed circuit, or burn-in boards; placing the burn-in boards into a housing with a chamber having an environment, particularly temperature, that is closely controllable; applying electrical test signals to each IC package on each burn-in board while uniformly subjecting the IC packages to the same temperature for a specific period of time; removing the boards from the chamber; and unloading the IC packages from the burn-in boards for sorting, distribution, and use or disposal.
An example of a "burn-in" chamber of the prior art holds up to seventy-two burn-in boards, each board holding numerous hundred IC packages. It is well known that there is a need to have an access opening to the burn-in chamber to allow loading and unloading of burn-in boards. Further, the chamber must have a door, or access opening covering, to cover and uncover the access opening. Prior art burn-in chambers are shown, for example, in U.S. Pat. No. 5,359,285 to Hashinaga et al., and U.S. Pat. No. 5,003,156 to Kilpatrick et al. Problems have been encountered with typical prior art burn-in chambers, which have doors that swing open outwardly from the front of the chambers. Significant space requirements are necessary to allow opening of the front swinging doors and loading and unloading of burn-in boards, which are typically transported on rolling carts. Ergonomic problems have been encountered by personnel loading and unloading the burn-in boards around the chamber doors, which typically requires the physically awkward and physically stressful movement of turning around to transfer boards between a burn-in board cart, or holder, and the chamber.
In another aspect of burn-in chambers, it is important to control the temperature within the chambers because slight variations in temperature can have a significantly detrimental effect on burn-in. In typical burn-in chambers, the temperature of the IC packages is controlled by directing a continuous flow of temperature controlled air over the boards during burning-in. The air absorbs the extreme amounts of heat generated by the IC packages mounted on the burn-in boards and is thereafter removed from the chamber. For burning-in powerful, high dissipation IC packages, for example, the air flow over the burn-in boards must be of a high volume, such as at a rate of over 2,600 cubic feet per minute, to effectively remove the heat generated by the IC packages.
For effective burn-in of IC packages, the temperature controlled air should generally uniformly flow over the burn-in boards and IC packages. However, spaces or gaps are formed between the burn-in boards and the access door and interior walls of the typical burn-in chamber, creating an air flow path of least resistance not over the boards. Air also deflects off of the burn-in boards and into the gaps. The gaps thus cause a reduction in the necessary airflow over the IC packages on the boards. The undesired air flow in gaps between the burn-in boards and the interior walls of the chamber is minimized in prior art chambers by filling or blocking the gaps with various devices, such as air deflectors, baffles or insulation. The access doors of typical prior art devices, however, are not equipped for effectively filling or blocking the gap formed between the door, or covering, and the burn-in boards inside the chamber, while also avoiding the ergonomic problems described above.
Problems similar to those described above also exist with doors for other types of devices used for stressing and testing electronic circuit components and other types of devices having environmentally controllable chambers used for other purposes and in other fields, such as convection-type ovens.
Thus, there remains a need for an environmentally controllable chamber covering, or access door, that does not swing open outwardly from the front of the chamber and has an expandable portion capable of extending into the chamber and sufficiently filling or blocking the space in the chamber adjacent the chamber covering. Preferably, the chamber covering will be easy to move between open and closed positions and the expandable portion will be easily and controllably expanded and retracted. Especially well received would be a chamber covering that requires minimal space around the chamber for opening and closing the covering, such as a covering that moves upwardly and downwardly, and does not require burn-in board loading/unloading personnel to have to turn around to load and unload the chamber. Ideally, the covering could be used with a device having multiple chambers or chamber openings, could be moved into various intermediate open positions and used in conjunction with apparatus for automated loading and unloading of the materials (such as IC packages) placed in the chamber. Further, it would be beneficial for the device to be used to retrofit existing environmentally controllable chambers.